what does it mean when you HAVE to provide UV coordinates using a Texture Coordinate node (to apply materials)?
You don't normally connect a UV socket to a Normal socket, the Normal socket is generally used for displacement or bump type of effects using either a texture or a normal map.

The fact that you connecting the UV socket to the Normal input of the material worked is probably just a coincidence, and a side effect of the fact that you mesh probably has some sort of geometrical glitch or wrong facing normals.

Try entering edit mode and clearing or recalculating your normals be selecting all faces and pressing Ctrl + N and see if that solves the problem.

Have in mind that this may destroy any custom normals your model might have (if any).